It seems by the way Luke introduces the story that he felt compelled to tell his readers that it is about the need to pray always.

What is a “Parable”?

Definition: “At its simplest a parable is a metaphor or simile drawn from nature or common life, arresting the hearer by its vividness or strangeness, and leaving the mind in sufficient doubt about its precise application to tease it into active thought.” (C. H. Dodd, The Parables of the Kingdom, New York: Charles Scribner’s Sons, 1961, p. 5)

Implications of this definition:

The meaning of most parables is not so obvious, or at least it shouldn’t be. If we assume we know what Jesus is talking about, we are probably missing the main point; if we are too familiar with the story (having heard it so often before), we might not think carefully enough about its real meaning.

Most parables contain some element that is strange or unusual. They should cause you to say, “Wait a minute! That’s not how farmers do their work! That’s not what kings usually do! That’s not what normally happens in nature!” And this strange element should cause you to think!

Parables do not define things precisely, but rather use comparisons to describe some aspect of how God acts or interacts with human beings. Yet to say “A is like B” does not mean that “A is identical to B in all respects”; so one should be careful not to misinterpret or misapply the parables.